New high resolution pollen, charcoal and sclerochronological records from Northern Patagonian lakes

BIANCHI, MARIA M.; SOLDATI, ANALIA L.; JACOB, DORRIT E.; SCHÖNE, BERND

Bonn, Germany

Congreso; 12th International Palynological Congress and 8th International Organisation of Paleobotany Conference; 2008

University of Bonn

Quaternary palynologists have been active for almost a century in NorthernPatagonia. Pioneer studies relying on pollen as a regional stratigraphic tool gaveplace to interpretations of the vegetation response to environmental and climaticchanges since glacier retreat in the region ca. 17,000 cal years B.P. More recently, avariety of proxy-records were added to the initial pollen sequences and palaeoclimatestudies were enhanced under international collaborative research programs. Studiesconcentrated on sensitive spots within two major watersheds, discharging either tothe South Atlantic Ocean (Río Limay) or to the South Pacific Ocean (Río Manso) andintroduction of new methods for recovery and analysis of lake sediments facilitatedthe obtainment of lake sediment proxies including sedimentological, geochemical andbiological data. Therefore, a more detailed picture of landscape and ecosystemtransformations could be achieved which suggests a steeper west-east precipitationgradient during the Full Glacial, a reorganization of the regional drainage systemduring the Late Glacial and significant shifts of the forest-steppe ecotone duringHolocene times. This well-studied area therefore provides an excellent framework totest and develop new high-resolution proxy archives which will complement andextend the existing proxy-records. We are evaluating shells of the fresh water clamDiplodon ch. patagonicus from Northern Patagonian lakes for their potential as anenvironmental proxy archive and complement this study with high resolution pollenand charcoal studies of short sediment cores from the same lakes. The mussel shellsconsist of aragonite and grow in annular increments reaching a life span of more than90 years. Modified dendrochronological methods (Schoene et al. 2002) showperiodicities of 2.5, 7 to 9 and 15 years which can be matched with recurring climaticparameters in the area.High resolution pollen and charcoal records from short cores covering the water-mudinterface and dated with 210Pb and 137Cs, show fluctuations in Nothofagus –Austrocedrus forest environments as well as regional (background) charcoal trendsbut no evidence of fires (peaks) during the last century at the two studied lakes inboth watersheds.Schoene et al. (2002): The Veliger 45(1): 45-54.